Wallet Service

A Go-based wallet service offering APIs for managing user wallets, including deposit, withdrawal, and fund transfers. Built using the Gin framework and PostgreSQL, with a focus on concurrency, data integrity, and idempotency.

Overview

Design Highlights

• Concurrency Control: PostgreSQL row-level locking with the NOWAIT option prevents deadlocks and ensures data consistency.
• Idempotency: Idempotency keys handle duplicate requests gracefully.
• Atomic Transactions: All operations are atomic within transactions, maintaining integrity.

Setup & Running the Service

1. Clone the Repository

git clone https://github.com/ftteh/golang-wallet-api
cd golang-wallet-api

2. Install Docker & Docker Compose

Ensure Docker and Docker Compose are installed. You can download them from:

https://www.docker.com/products/docker-desktop

3. Start Services

docker compose up

This starts the wallet service along with PostgreSQL.

4. Access the API

• API Base URL: http://localhost:8080
• Swagger Docs: http://localhost:8080/swagger/index.html

5. Stop Services

docker compose down

Testing

Automated Testing

go test -v ./...

Manual Testing

Use Swagger UI at http://localhost:8080/swagger/index.html to interact with the API.

Code Review Guidance

Focus on the following:

• Concurrency Handling: Implementation of row-level locking and retry logic.
• Idempotency: Correct use of idempotency keys.
• Code Structure: Organization, clarity, and maintainability of the code.

Concurrency Handling – Technical Explanation

• Database Row Locking: Uses GORM's clause.Locking{Strength: "UPDATE"} to lock rows during transactions.
• NOWAIT Option: Fails fast when encountering locked rows to prevent deadlocks.
• Retry Logic: Retries transactions that fail due to locks using exponential backoff.
• Idempotency Keys: Prevents duplicate transactions by associating a unique key with each request.
• Atomic Transactions: Ensures that all steps in a transaction either succeed together or fail together.

These techniques ensure the service remains safe and consistent under high concurrency.

Accessing the Database

Option 1: Using pgAdmin

• Host: localhost
• Port: 5433
• Maintenance database: walletapp
• Username: walletuser
• Password: walletpass

Option 2: Using psql via Docker

docker exec -it wallet_postgres bash -c "psql -U walletuser -d walletapp"

This opens a PostgreSQL shell inside the container.

Areas for Improvement

• Increase test coverage, especially for edge cases and errors.
• Improve logging for easier debugging.
• Add authentication and authorization to secure API endpoints.
• Implement encryption where appropriate.